The present invention relates to a vacuum heat-insulating panel having heat insulating and sound blocking features, and a method of manufacturing the same.
Conventionally, there have been developed various panels and blocks having their respective inner spaces retained in vacuum to attain enhanced heat insulating capability. A vacuum heat-insulating block has its surface covered with flexible substance and its inside depressurized to provide a vacuum pack configuration, and such a configuration leaves the block unsatisfied in strength. To overcome this disadvantage, an improved vacuum block has its surface bonded with a rigid surface material to enhance its heat insulating property and rigidity. An improved heat-insulating panel is designed in a sandwich-like multi-layered configuration with a core element having a surface element superposed at its front and rear surfaces, retaining the inside of the core element in vacuum condition to attain enhanced properties of thermal break and strength.
A vacuum heat-insulating block or a vacuum panel does not transmit sound and thus advantageously has a sound blocking property and a heat insulating property. However, in an exemplary panel with the core element formed of continuous foam material which transmits sound, it has been found that heat and sound transmissibility levels are raised depending on the density of the core element, and therefore, it is desired to develop the core element for the vacuum heat-insulating panel that is reduced in density but enhanced in strength.
In view of obtaining the heat insulating and sound blocking features, the core element is desirably fabricated of a substance of low density. On the contrary, the core element must be sufficiently strong especially against compression and shearing forces, and for that purpose, it should desirably be fabricated of a substance of high density. It has long been desired to selectively obtain substances for the core element (e.g., continuous foam material) that meet such contradictory requirements.
Thus, a honeycomb core of assembled basaltiform or cylindrical cells is devised, which is suitable to be used as the core element of the vacuum heat-insulating panel because of its high compression and shearing strengths in contrast with relatively low density. The multi-layered panel having the core element in honeycomb structure and surface materials superposed at its front and rear sides is generally known as xe2x80x9choneycomb panelxe2x80x9d, and especially, for such honeycomb panel used for structures, the honeycomb core serving as a core element is fabricated of a selected material excellent in shearing strength and shearing rigidity while the surface element is made of a material superior in tensile stress and compression strength, so as to implement increased flexural strength and rigidity.
In order to further add a heat insulating property to such structural honeycomb panel, the honeycomb core serving as the core element has its in side cells retained in vacuum condition and has its opposite sides superposed with surface materials into a multi-layered configuration so as to accomplish the improved vacuum heat-insulating panel.
Thus, the vacuum heat-insulating panel inherits the strength and rigidity from the honeycomb panel while retaining the inside of the honeycomb core in a vacuum condition.
This type of honeycomb cores can be roughly classified into those having air-permeable cells and those having non-permeable cells, depending on the material of which they are made.
With the air-permeable honeycomb core, all the cells in the panel serve as spaces defined separately but communicating with one another, and thus, a panel can be easily manufactured which has all the inside cells of the honeycomb core in vacuum condition.
With reference to FIG. 12, a method of manufacturing the vacuum heat-insulating honeycomb panel incorporated with an air-permeable honeycomb core will now be described.
Referring to FIG. 12(a) illustrating a set-up procedure, an air-permeable honeycomb core 11 is mounted on a work table 20, having its upper and lower surfaces superposed with bonding films 13 and surface materials 15 in this order. Simultaneously, edge columns 17 are positioned to prevent the ends of the honeycomb core from collapsing.
Referring to FIG. 12(b) illustrating a heating, pressing, and bonding procedure, the upper and lower surfaces of the layered panel element are heated and pressed by a hot press 25 to fuse the bonding films 13 and consequently bond the surface materials to the honeycomb core 11.
Referring to FIG. 12(c) illustrating a depressurizing and sealing procedure, air is pumped out of the inside space of the honeycomb core 11 through a vacuum port 19 connected to a vacuum pump to depressurize the space. After the evacuation of air, the vacuum port 19 is sealed.
In an embodiment disclosed in Japanese Patent Unexamined Publication No. H11-280199 where an air-permeable honeycomb core has its opposite sides bonded to the surface material with the bonding films to depressurize the inside space into a vacuum condition, after air in the inside space of the core is pumped out into vacuum, the edge columns 17 support the honeycomb structure at the opposite edges to prevent the ends of the core from collapsing by the atmospheric pressure.
An example of depressurizing performed before the bonding procedure is shown in FIG. 13.
Both the upper and lower ends 11a of the honeycomb core 11 sufficiently withstand compression by the atmospheric pressure, but lateral ends 11b of the honeycomb core collapse by the atmospheric pressure.
As has been described, the air-permeable design of honeycomb core and the process of developing a vacuum condition after bonding the surface materials thereto advantageously enable the whole core to be evacuated into vacuum, but due to the air-permeability of the cells, the vacuum condition of the whole panel is lost when even a part of the panel loses its air-tight seal, which results in the panel losing the heat insulating and sound blocking features. Additionally, after the layered elements are integrated into a panel, it is impossible to cut it into various shapes or to punch a hole there through. Thus, the panel must be created into a wide variety of dimensions and designs depending on various applications.
An embodiment incorporated with the non-permeable honeycomb core will now be described.
It is a basic requirement that the honeycomb core used for structural members should be rigid. However, if a heat insulating property is especially required, a non-metallic honeycomb is used due to its poor heat conductivity. Particularly, the non-metallic honeycomb core, when used for manufacturing a high-strength panel, is first bonded to other elements into a multi-layered panel element, and thereafter impregnated with fused resin solution while being under spreading and tensile forces to gain increased shearing rigidity, and hence, during such manufacturing procedure, the honeycomb core loses air-permeability.
In the vacuum heat-insulating panel incorporated with the non-permeable honeycomb core, the honeycomb core has its cells defined independent of one another, so the resultant panel would not lose its heat insulating and sound blocking properties even if apart of the panel is damaged to degrade air-tight sealing. Cutting the panel or punching a hole thereto causes the panel to merely locally lose its inherent properties, but advantageously, the panel, as a whole, still retains the preferable properties.
This enables the vacuum heat-insulating high-strength panel to be manufactured in large dimensions and then cut into pieces of required dimensions or to be provided with a hole, depending on applications.
However, there arises some problem with the procedure of evacuating the whole non-permeable honeycomb core into vacuum. Specifically, since the cells of the honeycomb configuration are defined independently, when pumping air out of all the cells to leave the inside space of the panel in a vacuum condition in the course of the manufacturing process, the coating materials and surface materials are depressed due to the atmospheric pressure so that the surface materials or the bonding films block the apertures of the cells to cause difficulty in further evacuating air therefrom.
Moreover, since the honeycomb core itself lacks air-permeability, the core must have its opposite sides bonded to the surface materials after having its inside evacuated into vacuum, but there also arises a problem that at a time when the inside space of the core is put in a vacuum condition, ends of both longitudinal and lateral extensions of the core collapse due to the atmospheric pressure, similar to the aforementioned case.
Japanese Patent Unexamined Publication Nos. H09-166272 and H10-89589 disclose improvements that have overcome the above-mentioned disadvantages, where during the procedure of evacuating the cells into vacuum, the coating materials, the surface materials, and the core element are all placed in a vacuum chamber and respectively set up in positions on a jig, and then, after a vacuum condition is developed in the chamber, the components are bonded together.
As to the technology, the vacuum chamber must be large enough to house the panel, and the chamber must be evacuated into vacuum each time the panel element is carried in or out. Thus, a fabrication of the considerably large panel of this type requires huge equipment, which leads to reduced working efficiency and increased manufacturing cost.
Furthermore, the honeycomb core has its inherent properties deteriorated over time if it has even very little air permeability, so it is desirable to seek for an achievement of non-permeability.
Accordingly, it is an object of the present invention to cost-effectively provide a large, high-strength vacuum heat-insulating panel incorporated with a honeycomb core of non-permeable independent cells by means of simplified equipment and procedures.
It is another object of the present invention to avoid any deformation of the opposite ends of a lateral extension of the core from the commencement of depressurizing into vacuum till the completion of panel bonding.
It is further another object of the present invention to ensure a long lasting integrity of air-tight sealing in the honeycomb core.
A vacuum heat-insulating panel according to the present invention basically consists of a core element evacuated into a vacuum condition and made of non-permeable material in honeycomb structure, a surface element, and an air-permeable bonding element fused to bond the surface element to the core element.
The bonding element may be either of woven or unwoven cloth made of adhesive fabric of thermoplastic resin, or may be a bonding sheet that has woven or unwoven cloth of adhesive fabric of thermoplastic resin overlapped with a film of thermosetting synthetic resin.
The surface element has its edges bent to provide protection covers, or alternatively, the surface element may have its opposed edges bent with sealing element laid over a gap between the opposed protection covers.
A method of manufacturing the vacuum heat-insulating panel in a multi-layered configuration with a vacuum core element overlaid and bonded with a surface element includes stepwise procedures of superposing the core with surface elements through adhesive interposed therebetween to produce a multi-layered element, covering the multi-layered element with synthetic resin film and evacuating air under the cover of the synthetic resin film into a vacuum condition to produce a vacuum core element, and heating and pressing the covered multi-layered element having the vacuum core element at its center to bond the surface element to the core by the adhesive, the core being made of non-permeable material in honeycomb structure, the adhesive being either woven or unwoven cloth of fibrous thermoplastic resin, the air inside the core being evacuated through pores in the woven or unwoven cloth during the step of evacuating air into a vacuum condition, and the adhesive being fused to bond the surface elements to the core during the step of heating and pressing.
The adhesive may be woven or unwoven cloth of fibrous thermoplastic resin superposed with a film of thermosetting resin into an adhesive multi-layered sheet, and during the step of heating and pressing, the film of thermosetting resin in the adhesive multi-layered sheet is fused and liquidized to fill clearances in a bonding interface between the core and the surface element. Alternatively, a bank may be provided at a lateral end(s) of the multi-layered element to reinforce the core. Otherwise, the surface element may have its edges bent to provide protection covers which reinforce the core during the step of evacuating air into a vacuum condition.